1. Field of the Invention
The present invention relates to a process for making carbohydrazide.
2. Description of the Prior Art
Carbohydrazide [NH.sub.2 NHC(O)NHNH.sub.2 ] has recently been found to be an effective oxygen scavenger for boiler system. See U.S. Pat. No. 4,269,717, which issued to M. Slovinsky on May 26, 1981. It has also been used as a cross-linker for elastic-type fibers.
This compound has been prepared by numerous methods. See F. Kurzer and M. Wilkinson "The Chemistry of Carbohydrazide and Thiocarbohydrazide" Chemical Reviews Volume 70, American Chemical Society pages 111-149 (1970). The usual method for making carbohydrazide in commercial quantities was to react a dialkyl carbonate and excess hydrazine in one step. The alcohol co-product was simultaneously distilled off at atmospheric pressure until the reaction was complete. Typically, the reaction lasted from about 4 to about 6 hours and the temperature of the reaction mixture was raised from about 95.degree. C. to about 120.degree. C. See E. Mohr, J. Brezinski and L. Audrieth "Carbohydrazide" Inorganic Synthesis, Volume IV, McGraw-Hill Book Company, Inc. (1953) pages 32-35.
This prior art process sometimes resulted in carbohydrazide products which contained large amounts of impurities. The identities and effects of these impurites are not well understood. However, they contaminate the product and lower the yield, as well as cause some batches of carbohydrazide to unexpectedly decompose within a few months. This decomposition may have contributed to preventing the large scale commercial usage of carbohydrazide in the past.
It is believed that the relatively high temperatures of this prior art process may contribute to the formation of these impurities by side reactions.
Furthermore, the useful technique of vacuum distillation could not safely be employed with this prior art process because of the excess amounts of hydrazine present. Hydrazine vapor in the distillation column might form explosive mixtures if the apparatus leaked and air were admitted.
Accordingly, there is a need for a process for making carbohydrazide which forms smaller amounts of undesirable impurities and is safe to use with vacuum distillation or similar techniques. The present invention is a response to that need.